I can understand this, really. It might be because...
My most disappointing game is Lightning Returns and or Final Fantasy XIII-2. I trusted Square and they disappointed me with this... garbage. At least, that's how I regard it. Even the games I didn't like so much weren't as bad as this one.
LR Complaints: The gameplay wasn't too bad, although all the sidequests really get to you after... around 10 minutes of playing or so. It just seems so absurd.
I also hate how you can't get experience from battles and only from said sidequests, forcing you to get the Doll of Power for Johnny Bearass or whoever the random badly designed NPC of the day with random accessories is.
The story was also ridiculous in both with some of the most badly written dialogue I've ever heard. Especially out of Caius Ballad, who I laughed every time he spoke and found him to sound like he was written by a 14 year old girl who likes emo goth things. I found it all to just stretch on my suspension of disbelief. None of the things they added made sense in the context of the FFXIII universe. It would've been better if they put all of these disjointed lore ideas (especially the time travel) in its own original thing, then the story would've made more sense.
I just found it to be so bad, that I fear for the future of FF installments. Hopefully, that was just a fluke and they'll be back up to tip-top shape for XV.
Ah, that felt good. Been wanting to say that for a long time. Sorry to those of you who are fans of these games, I can appreciate different opinions from mine. :3